UI: Assume RTMP if service has no protcol

UI/window-basic-settings-stream.cpp

@@ -566,7 +566,10 @@ QString OBSBasicSettings::FindProtocol()
 
 		obs_properties_destroy(props);
 
-		return QT_UTF8(obs_data_get_string(settings, "protocol"));
+		const char *protocol =
+			obs_data_get_string(settings, "protocol");
+		if (protocol && *protocol)
+			return QT_UTF8(protocol);
 	}
 
 	return QString("RTMP");